Milorad Dodik, President of Republika Srpska, speaks after the results of a referendum over a disputed national holiday during an election rally in Pale, Bosnia and Herzegovina, September 25, 2016. REUTERS/Dado Ruvic

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By Daria Sito-Sucic

SARAJEVO (Reuters) - Bosnia's chief prosecutor has summoned the president of the country's Serb Republic for questioning after he defied the top court by holding a banned referendum on whether his autonomous region should mark a national day.

The vote on whether the Serb Republic should celebrate a "Statehood Day" on Jan. 9 was widely seen as Dodik's attempt to explore the limits of the region's independence from authorities in Sarajevo, the capital.

"It is impossible to expect someone to build a state based on arresting political opponents," Dodik said.

"The referendum will remain an undisputed fact and it does not matter if Milorad Dodik is held responsible or not."

Bosnian Serbs voted overwhelmingly on Sunday in favor of the holiday, which Bosnia's Constitutional Court had ruled discriminatory against Muslim Bosniaks and Catholic Croats because it coincided with a Serbian Orthodox Christian festival.

The United States condemned the "illegal referendum" and would support local institutions as they sought to hold the Bosnian Serb leadership accountable for undermining the rule of law, the U.S. State Department said in a statement.

Western powers fear the vote could bring about instability in the country which only last week made its first major step toward joining the European Union.

On Monday the Office of the Disciplinary Council, a national judicial body, called for Goran Salihovic, the chief prosecutor behind the summons of Dodik, to be dismissed for alleged violations.

"The reason is that I have opened the investigation against Milorad Dodik, who has received a summons for the first time ever," Salihovic said in a statement sent to Reuters.

The Bosnian conflict was ignited by Serbs' declaration on Jan. 9, 1992, of an independent "Serb Republic" in the north and east of Bosnia. The territory became the autonomous region of the same name under the peace agreement which ended the war.

Most Bosniaks and Croats opposed Sunday's referendum out of fear that the Serb Republic could be preparing to secede, destroying the delicate federal structure put in place after the war.

A Western diplomat told Reuters that secession for the region, which has a third of Bosnia's population of 3.5 million, remained a "red line".